Some features of the calcium metabolism of the shore crab ( carcinus maenas pennant)

One of the features of the Arthropoda is the possession of a stiff outer covering of chitin secreted by the epidermis. This outer covering is cast periodically, and it is a characteristic of the group that increase in size takes place immediately after ecdysis or moulting of the old skin. During this period the new skin is soft and extensible. In many of the higher Crustacea, this chitinous covering is hardened by the deposition in it of calcium salts, chiefly the carbonate and phosphate, thus forming a protective exoskeleton. Under this term are included the endophragmal skeleton and the partially calcified foregut.